Using the HCl-Giemsa banding technique, the total proportion of condensed chromatin was determined by planimetry in 23 plant species and was found to vary from 14–77%. Comparison of condensed chromatin values withDNA content indicated that the latter was involved in determining the interphase nuclear structure. The actual amounts of differentDNA components in these species were estimated in terms of picograms. Statistical analysis of condensed chromatin values with quantities of different types ofDNA sequences showed the best correlation with highly repeatedDNA sequences, suggesting that these sequences could be playing an important role in governing the species-specific chromatin condensation in plants. The amount ofDNA packaged per unit length of chromatin was also shown to be a determinant of interphase nuclear structure.